The way the deal is structured, even if they buy the team, they still must put the TV rights up for bid, due to Tanenbaum's stake and other shareholders.

So by buying MLSE's stake of the franchise you gain nothing media wise. Other parties can still bid up the rights, and Bell or Rogers will be paying indirectly back to the Tanenbaum and other shareholders for those rights. Depending on the size of their pie, it represents a significant leak of funds.

It's a little better for rights holders, but not worth putting in billions into the asset for the sort of gain involved. If it was outright ownership, they would be more than interested.

(If Larry and the other shareholders could be persuaded to give up their stake, or rework the tv rights acquisition process maybe they would bite... but why would the other shareholders agree to get jacked on TV rights?)